VITEEE 2009 Paper

Let listener go from A → B with velocity (µ).

And the apparent frequency of sound from source A by listener using Doppler's effect,
n'=n(

v−vo

v+vs

)⇒ n'=680(

340−u

340+0

)
The apparent frequency of sound from source B by listener
nn=n(

v+vo

v−vs

) =680(

340+u

340−0

)
Listener hear 10 beats per second.
Hence, n'' - n' = 10
⇒680(

340+u

340

)−680(

340−u

340

)=10
⇒ 2(340 + u - 340 + u ) = 10 ⇒ u = 2.5 ms−1